Fast developing supercapacitor technology may make
batteries last longer in consumer gear as well as hybrid buses. Thin-film
battery technology, pressed ceramic solid state batteries, and silicon anodes
also all make progress.

Solid state batteries are finally seeing real revenues in some specialty niches, but scaling the
technology to more demanding mainstream applications will still require significant
investment. Battery makers are starting
to look at silicon electrodes to improve workhorse lithium-based battery
technology. But the technology most likely to significantly impact energy
storage markets in the near term is supercapacitors, where there are plenty of
opportunities for better processes and materials.

“Supercapacitors are now at the tipping point,” says Peter Harrop,
chairman of IDTechEx. “They may be a way to leapfrog
battery technology.” He notes that it is
already a real market, revenues are growing at 30 percent a year, and
technology is improving rapidly. Typically the electrostatic charge storage in supercapacitors
charges and discharges fast, but stores much less energy than electrochemical batteries.
“It used to be true that energy density was lower, but with supercapacitors,
whatever you knew last week has changed this week,” says Harrop. “Five companies now say they can make a
supercapacitor with the energy density of a battery, up to 20-40Wh/kg typical
of a lead-acid battery, and some are targeting 130Wh/kg, approaching the
160Wh/kg of an exceptional lithium-ion battery.” The supercapacitors remain more expensive, but since
the electrostatic device life is much longer than electrochemical batteries, they often have lower total cost
long term.

Main markets so far are to supplement batteries when extra power
is needed, to make the batteries last longer, or for short-term backup when other power
fails. Electric or hybrid buses use them for extra power to go up hills, and for
the instant starts in “stop-start”
technology to make the batteries last longer. Buses also use
them to open the doors in an emergency if the power fails. Trucks use them for
sure starting in cold weather. Wind turbines use them to set the blades to
protect from damage in big winds if the power fails. Mobile phones will use
them for more powerful flash for lighting at greater distance, or for
supplementing demands for power for wi-fi, to save the battery or allow use of
a smaller one or cheaper one.

These growing markets are spurring demand for better performance
from the relatively simple devices of porous carbon coating on aluminum foil,
with the two sides separated by a membrane. And there’s plenty of room to improve
the processes and materials. Thinner foil of a few microns thickness could
potentially reduce cost and increase overall energy density. There’s potential for better processes to
handle the thinner foil, and to roughen its surface. Better ionic liquids may
improve the electrolyte. And the carbon coating, now made largely from burnt
coconut shells, will likely move towards nanostructured films and ultimately to
graphene for higher surface area, but while controlling pore shape to avoid
sharp edges. More environmentally
friendly alternatives to acetonitrile could be possible. “Everything’s up for
grabs,” says Harrop.

Leading supercapacitor maker Maxwell
Technologies says government regulation to limit carbon emissions from
vehicles has been a big driver of demand,
particularly for the stop-start function for the hybrid
bus market. “Demand is also starting to grow for
megapixel cameras,” says Earl Wiggins, Maxwell VP of operations, noting that
battery makers are looking at ways to improve battery
performance in consumer electronics by
combining the battery with a thin
supercapacitor.

Cost has come down dramatically in recent years with higher
volumes and improved equipment. While most suppliers make the carbon electrodes by
wet coating, Maxwell uses
a dry process, mixing the carbon powder with a binder, then pressing the mix into a <100µm
film on foil with heat and pressure. “The dry
process is cheaper, more controllable, and solvent free,” says Wiggins, noting
the major cost of running the usual drying furnace for the wet process. Like the rest of the industry, the company has found that carbon from coconut shells happens to provide fine soot of ~10µm particles with many pores, which increase surface area to 10-20x the particles’ diameter. “You want a waste product as
the carbon feedstock for the best cost structure,” he adds.

Consumer electronics applications will need
higher power density, Wiggins notes, and key to that is very thin films. Maxwell
is working on improving pressure and gap control of its deposition process,
aiming to reduce the thickness of its dry film by half. But wafer-fab type
sputtered thin films could also be a solution, although the films would need to
be of softer carbon than the usual sputtered diamond type, and would need
better pore structure. Best paths to
increase energy density are to increase the voltage by doping the carbon or
changing the material, and by improving the ionic liquid electrolytes. Getting
voltage up from the current ~2.7V to around 4.0V would also allow most consumer
electronics products to use only one supercapacitor cell instead of two,
helping to bring down costs. Packaging
for consumer electronics will be another key challenge, to protect the device for
volume wave or reflow soldering, as the electrolyte tends to break down in heat
above about 85°C. And there’s room for improvement from closer integration of
the supercapacitor with the battery as well, instead of just putting two
separate devices into a bigger package.

Low-Power Solid State Batteries Find
Some Niches

On the battery side, products using
disruptive thin-film or printed battery
technology will come to a $6.5 billion market by 2016, largely from sensors,
medical implants and powered smart cards, projects NanoMarkets. “These batteries
have found some high value niches,” says Lawrence Gasman, principal analyst of NanoMarkets. “But they all have to
compete with coin cell batteries that cost basically nothing. The sector is
kind of in limbo.”

Source: NanoMarkets,
“Thin-Film and Printed Battery Markets – 2012"

Real markets have developed for wireless
sensor networks, thanks to significant economic benefit from savings on copper
wiring and energy usage in buildings, and from improving asset management and
process monitoring in factories. But
unit volumes for thin-film batteries perpetually recharged by PV or other
energy harvesting remain very small. Automakers, for example, are all using
active (powered) tags to track assets, says Raghu Das, CEO of IDTechEx, but the total market remains
a only a few million units, and many of those units remain powered by
conventional coin cell batteries. There’s a compelling case for using
rechargeable thin-film batteries with energy harvesting instead, since it’s
considerable trouble to locate the asset and replace the battery when it dies.
And for places where replacement is difficult the total cost of using a longer-lasting thin-film battery may
well be lower. But the higher upfront
costs still make it a hard sell. “It’s been difficult to educate users about
replacement costs in 5 to 7 years — it’s not their problem,” notes Das. “The successful companies in the wireless
sensor market are largely those making the systems. Thin-film batteries are
seeing slow uptake.”

Powered smart cards — where coin cells are too thick to use — are
another likely market, which NanoMarkets now expects will reach $960 million by
2016. Gasman notes that battery suppliers, like market leader Solicore, with
its hybrid lithium polymer battery with coated electrolyte, are getting real
revenues from this market. The powered cards so far are mostly used to generate
one-time passwords for added security for credit and bank card transactions
overseas, where the banks can save by preventing fraud. Bank of America, eBay
and Mastercard in the U.S. all now issue these cards, but both banks and
consumers remain slow to take them up.
Das says sales are likely still only in the tens of thousands of units.
But with the increase in Internet banking, and increasing security requirements
from European regulators now requiring one-time passwords for online
transactions, the smart cards start to look increasingly attractive. Das notes
he now has to use a clunky calculator-like device to generate a passcode to
sign in online to his bank in the U.K., making a card he could carry in his
wallet look very attractive.

Higher powered cards, however, may have more applications. Infinite Power Solutions says powered
cards are among its early design wins using its sputtered thin film batteries,
with takeup particularly in secure identification, which they expect markets of
at least 10,000 units. “Powered cards have been held back from wide industry
adoption by cost and the limitations of the short-lived non-rechargeable
battery used as a power supply,” says Tim Bradow, VP of marketing at Infinite
Power Solutions (IPS). “They didn’t have
enough power or lifetime capacity to run a fingerprint sensor, and now people
want a display, a microprocessor with reasonable speed and RF connectivity too.
But with all that functionality added, the card becomes too costly to throw out
after only two years when its primary battery dies. Our higher power density,
rechargeable thin-film batteries can solve these problems.”

Other applications seeing traction for the thin-film batteries,
says Bradow, are powering health and fitness wireless sensors worn on the body
to monitor heart rate and the like, where the thin, flexible battery fits more
comfortably and invisibly on the body under the clothes than a bulky coin
cell. There’s also some demand for use
with PV energy harvesting for indoor wireless sensor networks in commercial
buildings for energy savings, and for backup power for real-time clocks.
Improvements in the production process and yields over time have brought volume
prices down to the $4-6 dollar range for the “postage stamp”-sized batteries.

Scaling up Solid-State Battery Technology Remains a Challenge

“The real challenge in making solid-state thin-film batteries — and
in potentially extending the technology for more demanding applications like
mobile phones — is the capital equipment,” says Bradow. “It doesn’t exist.” IPS has
modified LCD sputtering equipment to deposit on strips of metal foil, by laying
out the strips on a pedestal in the chamber and using shadow masks to define
the regions for deposition of the LiCoO2 electrode and LiPON electrolyte, then
depositing the Li by thermal evaporation.
This requires specialty material targets, where there’s been little
motivation to date for suppliers to invest in improved technology for the
relatively small market. Post deposition the strips are laminated together with
metallized flexible circuit material for hermetic packaging, and then laser
singulated.

Bradow says the company has now improved the deposition process to
produce a thicker cathode to store more energy and maintain sufficient
stability for charging cycles, so it believes the technology could be scaled up
for more demanding applications such as mobile electronics. It figures these
thick cathodes could be sputtered on both sides of thin metal foil in a
roll-to-roll process, and then stacked together, for roughly 25 percent better
energy density and much higher power capability than the prismatic lithium ion
batteries now used in cell phones. “But
scaling up the process and building the fab for volume production would cost
millions,” says Bradow.

IPS suggests a new and more economical solution to scale up
solid-state batteries may be a powder-formed ceramic battery, developed by its
CTO Bernd Neudecker and director of Engineering Shawn Snyder. Neudecker was
also one of the co-inventors of the solid-state thin film battery technology at
Oak Ridge National Laboratory in mid 1990s. The new ceramic approach improves
energy density, in part by eliminating the substrate and
minimizing the packaging. Researchers have taken known materials with good
performance in other battery types, done some additional post-processing of
them into nanoscale forms, then compressed them into stratified layers using
off-the-shelf ceramics pressing equipment.
The current lab product reportedly
has twice the energy density of Li-ion batteries, or 1000Wh/l in a
1mm thick coin-type battery. “We think
this could scale to larger cells, but it would need custom equipment to
prototype it to see what’s possible,” says Bradow. “We’re in the final months
of optimizing the chemistry for a proprietary product at a customer’s request,
but are also announcing a more generic commercial version, and hope that
companies interested in working on this will contact us for more details.”

In other solid-state battery developments, auto battery
startup Sakti3 appears to be moving towards starting thin-film
production, as it’s been advertising to hire an assortment of vacuum process
engineers for sourcing and maintaining thin-film coating equipment, and for
process development. Meanwhile, however, local Florida newspaper reports
say the other larger-scale US thin-film battery maker Planar Energy has run
short of funding and largely stopped operations and is looking to license its
solution-processed, high-energy density thin-film technology.

One of the best options for major improvement in lithium-ion
batteries may be silicon, which theoretically absorbs up to 10x more lithium
than the carbon commonly used in battery anodes now. Unfortunately, the silicon absorbs so many
lithium ions in discharge of the battery that it swells to several times its
original size and then contracts again during charging, so it degrades too
quickly to be of any use.

University researchers and startups are working on plenty of
exotic solutions using silicon nanowires or nanotubes with various coatings to
improve silicon’s stability, but 3M
has a more evolutionary approach that’s actually moving into production and
sampling product to battery makers.
Chris Milker, business manager for battery materials in 3M electronics
markets materials division, says 3M’s silicon alloy powder combines silicon
with carbon in an anode composition that can potentially double the energy
density compared to graphite, and control swelling for improved cycle
performance. But battery makers will limit risk by adding low loadings of
silicon at first to their fairly standard graphite and binder coatings, to gain
about a 6 percent improvement in capacity in consumer electronics batteries,
although they’ll also need to make some adjustments in their battery cell
designs. Higher loading of silicon alloy can reportedly could bring a ~12
percent improvement in battery capacity.

Source:
3M

The silicon alloy powder uses micron-sized particles for
optimizing packing and energy density, and a low surface area to maximize
thermal stability and minimize irreversible capacity and parasitic
reactions. “We’ve found that
nanomaterials don’t perform that well — they’re too reactive,” says Milker. The
company is now working on higher capacity cathode materials to match the
silicon to improve performance further, focusing on nickel-manganese-cobalt
with a core-in-shell approach, combining high-energy-density core materials
with a high-voltage, stable shell for improved cycling. An optimized pairing has been demonstrated to
give a 44 percent energy improvement in automotive batteries and 27 percent for
consumer products, says Milker.